1. Field of the Invention
The present invention relates to information processing for processing information of a plurality of measured heights respectively corresponding to a plurality of measurement points on a surface of a substrate held by a chuck.
2. Description of the Related Art
Recently, circuit patterns on semiconductor devices have been increasingly miniaturized, and the resolution of exposure apparatuses that transfer the patterns onto wafers (also referred to as substrates) has been improved using higher numerical apertures (NAs). However, higher resolution leads to a smaller depth of focus, and requires more correct focusing. Therefore, local defocuses caused by foreign substances adhered to the bottom surfaces of the wafers or wafer chucks that hold the wafers in the exposure apparatuses may become a problem. It is common knowledge that, in such exposure apparatuses, the surface shape (height distribution) of a wafer in a shot area is measured by obliquely projecting light onto the top surface of the wafer so as to form a light pattern thereon and by obliquely illuminating a photo detector with the light reflected from the top surface so as to re-form the light pattern thereon. Japanese Patent Laid-Open No. 2006-300676 describes a method for detecting foreign substances by calculating a surface (approximate surface) that approximates a surface in a shot area from the height distribution thereof and determining separations of the measurement results (heights) from the approximate surface.
The top surface of the wafer needs to be entirely scrutinized so that foreign substances causing the local defocuses are found, and needs to be measured at a large number of measurement points. As the foreign substances to be detected become smaller, the number of measurement points is increased. In addition, the size of areas for determining an approximate surface as described in Japanese Patent Laid-Open No. 2008-140814 needs to be further reduced, resulting in a reduction in processing speed.
It is preferable that the foreign-substance detection be performed immediately after the exposure and that necessary measures be taken. If the removal of the foreign substances, in particular, from the wafer chuck is delayed, the foreign substances may correspondingly cause focus failures. For this reason, a method for swiftly and accurately inspecting a foreign particle has been required.